Neuregulin (NRG; heregulin, HRG), also known as glial growth factor (GGF) and new differentiation factor (NDF), is a kind of glycoprotein with a molecular weight of 44 KD. As the ligand of tyrosine kinase receptor of ErbB family, neuregulin is responsible for cell signaling. NRGs family has four members: NRG1, NRG2, NRG3 and NRG4 (Falls et al., Exp Cell Res.284:14-30,2003). NRG1 plays an important role in nervous system, heart and breast. It is also evidenced that NRG1 signal transmission plays a part in the development and function of other organ systems, as well as in the pathogenesis of human disease (including schizophrenia and breast cancer). NRG1 has many isomers. The research in gene mutated mice (gene knock-out mice) indicates that isomers with different N terminal region or EGF-like domain have different in vivo functions. The present invention is based on NRG-1β.
NRG-1β is a transmembrane protein (Holmes et al., Science 256, 1205-1210,1992). The extracellular region is N terminal region, comprising immune globulin like domain (Ig-like domain) and EGF-like domain. The intracellular region is C terminal region. Under the action of extracellular matrix metalloproteinase, the extracellular region of NRG is in a free state after being cut off by enzyme, thus facilitate binding to ErbB3 receptor on the cell surface and activating relevant cell signal transmission.
EGF receptor family can be divided into four classes, including ErbB1, ErbB2, ErbB3 and ErbB4, all of which are transmembrane proteins with a molecular weight of around 180-185 KD. They all comprise an extracellular ligand-binding domain in N terminal region except ErbB2. They all have protein tyrosine kinase activity in intracellular C terminal region except ErbB3. ErbB1 is epidermal growth factor receptor while ErbB3 and ErbB4 are neuregulin receptors. Among these neuregulin receptors, only ErbB2 and ErbB4 are highly expressed in heart (Yarden et al., Nat Rev Mol Cell Biol, 2: 127-137,2001).
After NRG binds to the extracellular domain of ErbB3 or ErbB4, it induces the formation of heterodimers of ErbB3, ErbB4 with other ErbB receptors (normally including ErbB2) or homodimers of ErbB4, which results in phosphorylation of the receptor's intracellular region (Yarden et al., Nat Rev Mol Cell Biol, 2: 127-137,2001). The phosphorylated intracellular domain then binds signaling proteins inside the cell, thus activating the downstream AKT or ERK signaling pathway, and inducing a series of cell reactions, such as stimulation or depression of cell proliferation, cell apoptosis, cell migration, cell differentiation or cell adhesion.
NRG plays an particularly important role in the development of heart (WO0037095, CN1276381, WO03099300, WO9426298, U.S. Pat. No. 6,444,642, WO9918976, WO0064400, Zhao et al., J. Biol. Chem. 273, 10261-10269, 1998). At the early stage of embryo development, the expression of NRG is limited in endocardium, whereafter it is released to periphery myocardial cell by paracrine and binds to the extracellular domain of protein tyrosine kinase receptors ErbB4 on cytomembrane, the ErbB4 than forms a heterodimer with ErbB2. The formation and activation of the ErbB4/ErbB2 complex is essential to form the trabecular of sponge-like heart at early phase. The absence of any of the three protein genes for NRG proteins, ErbB4 and ErbB2, would lead to an embryo without trabecular and death in uterus at early development. WO0037095 shows that a certain concentration of neuregulin could sustainably activate ERK signaling pathway, promote the differentiation and growth of myocardial cells, guide the reconstruction of sarcomere and cytoskeleton at the site where myocardial cells are adhered to cells, improve the structure of myocardial cells and enhance myocardial cell contraction. WO0037095 and WO003099300 also indicate that NRG could be used in the detection, diagnosis and treatment of various cardiovascular diseases.
The following is a list of some prior art technical literature related to the present invention: 1. Cardiac muscle function and manipulation:WO0037095; 2. New application of neuregulin and its analogs: CN1276381; 3. Neuregulin based methods and composition for treating cardiovascular diseases: WO03099300; 4. Zhao Y Y, Sawyer D R, Baliga R R, Opel D J, Han X, Marchionni M A and Kelly R A. Neuregulins Promote Survival and Growth of Cardiac Myocytes. J. Biol. Chem. 273, 10261-10269 (1998); 5. Methods for treating muscle diseases and disorder: WO9426298; 6. Methods of increasing myotube formation or survival or muscle cell mitogenesis, differentiation or survival using a neuregulin: U.S. Pat. No. 6,444,642. 7. Therapeutic methods comprising use of a neuregulin: WO9918976; 8. Methods for treating congestive heart failure: WO0064400; 9. Holmes W E, Sliwkowski M X, Akita R W, Henzel W J, Lee J, Park J W, Yansura D, Abadi N, Raab H, Lewis G D, et al. Identification of heregulin, a specific activator p185erbB2. Science 256, 1205-1210 (1992); 10. Falls D L. Neuregulins: functions, forms and signaling strategies. Experimental Cell Research, 284, 14-30 (2003). 11. Yarden Y, Sliwkowski X. Untangling the ErbB signaling Network. Nature Reviews: Molecular Cell Biology, 2127-137 (2001).
Heart failure (HF) is a cardiac insufficiency syndrome caused by various heart diseases, including systolic heart failure (SHF) and diastolic heart failure (DHF). In 2008, the European Society of Cardiology (ESC) issued the Diagnosis and treatment guidelines of acute/chronic heart failure, and defined DHF as heart failure with preserved ejection fraction (HF-PEF). Systolic heart failure is a condition in which the heart with decreased myocardium contractility leads to cardiac output that cannot meet the needs of metabolism, tissue or organ hypo perfusion, pulmonary circulation and/or systemic circulation congestion. Heart failure with preserved ejection fraction (HF-PEF) often refers to diastolic heart failure due to the impaired diastolic relaxation of left ventricular and decreased myocardial compliance, myocardial cell hypertrophy and interstitial fibrosis of the left ventricular stiffness increases, which result in impaired diastolic filling, decreased stroke volume, increased left ventricular end diastolic pressure and the occurrence of heart failure. Epidemiological data from the American Heart and Lung Institute in 2006 showed that heart failure with preserved ejection fraction or diastolic heart failure accounted for more than 50% of the total number of patients with heart failure. Heart failure with preserved ejection fraction may exist alone, and also appear with systolic dysfunction. Heart failure with preserved ejection fraction is more common in elderly women with hypertension, diabetes mellitus and left ventricular hypertrophy.
Diastolic heart failure and systolic heart failure have similar symptoms and signs. Patients are usually with high blood pressure and other basic diseases. In the early stage of heart failure, unexplained fatigue, decreased exercise tolerance, heart rate increased 15 to 20 times per minute, may be an early sign of left ventricular function decrease. Then there may be the symptom of exertional dyspnea and paroxysmal nocturnal dyspnea, high pillow sleep. Abdominal or leg edema may occur in patients as the primary or sole symptom, while impaired exercise tolerance in patients occurs gradually.
Diastole is a more complex physiological process involving multiple factors than systole. Therefore, the diagnosis of heart failure with preserved ejection fraction or diastolic heart failure is more difficult than systolic heart failure. When the following conditions are met, the diagnosis can be made:
1. Typical symptoms and signs of heart failure;
2. Normal LVEF (or slightly decrease≥45%), normal left ventricular morphology;
3. There is evidence of underlying heart disease, for example, patients with hypertension have the evidence of left ventricular hypertrophy, left atrial enlargement, and left ventricular diastolic dysfunction in echocardiography;
4. Increased BNP/NT-ProBNP;
5. Echocardiography showed no valvular heart disease, and pericardial disease, hypertrophic cardiomyopathy, restrictive (infiltrative) cardiomyopathy etc. were excluded.
Heart failure with preserved ejection fraction or diastolic heart failure is associated with a variety of causes, in which the left ventricular pressure/volume mechanism is a more recognized pathogenesis. Patients with hypertension, hypertrophic cardiomyopathy, aortic stenosis have significantly increased ventricular end-diastolic pressure, and significantly reduced left ventricular capacity, which affect the ventricular filling, leading to the pressure and capacity curve left shift and the formation of centripetal remodeling. Long-term stress overload causes the occurrence of diastolic heart failure.
Ventricular diastolic function includes two phases, namely relaxation (initiative energy consumption process) and compliance of ventricular muscle. Relaxation of ventricular muscle is the change of heart cavity pressure per unit time during diastole, which is an initiative energy consumption process. Compliance of ventricular muscle is the change of heart cavity pressure caused by the change of unit volume during diastole, which is a passive filling process. Relaxation is the initiative diastolic of ventricular muscle at early diastole, the ability of the cardiac muscle fiber to recover to presystolic length and pressure, and is an energy dependent Ca2+ transport initiative energy consumption process, including the isovolumic relaxation and early diastolic rapid filling phase. The left ventricular relaxation is reflected by parameters including isovolumic relaxation (IVRT) duration, the maximum rate of pressure drop (−dp/dt), mitral E peak deceleration time (DT), etc. These parameters obtained by two-dimensional echocardiography and hemodynamic tests could be used to evaluate diastolic function of heart to a certain extent.
In addition, there is no specific treatment for heart failure with preserved ejection fraction. Present therapeutic guidelines include the use of standard therapeutic drugs for controlling blood pressure, reducing ventricular rate, reducing fluid retention (such as angiotensin-converting enzyme inhibitors/angiotensin II receptor inhibitors, β blockers and diuretics) which may improve systolic heart failure symptoms, /,but cannot improve the clinical symptoms and prognosis of heart failure with preserved ejection fraction. Finally, patients with heart failure with preserved ejection fraction or diastolic heart failure have a poor prognosis, a relatively high rate of re-hospitalization and repeated hospitalization, which increase the burden of the entire healthcare system. Systolic heart failure is the outcome of the development of diastolic heart failure. How to improve cardiac diastolic performance in the early stage of diastolic heart failure and prevent it from further deterioration, remains a great challenge in the treatment of diastolic heart failure.
There are no reports on the role of the neuregulin proteins related to heart failure with preserved ejection fraction or diastolic heart failure in the prior art technical literature. The present invention find administration of neuregulin to a mammal can significantly improve the symptoms of heart failure with preserved ejection fraction, and neuregulin can be used for preparing drugs for preventing, treating or delaying heart failure with preserved ejection fraction in a mammal.